This invention relates generally to a method for controlling the drive mechanism of a utility vehicle having a power take-off shaft, and, more particularly, to a controller for the driving mechanism of tractors, self-propelled agricultural machines, municipal utility machines, and self-propelled construction machinery.
In use as a utility machine wherein the implement pulled or mounted by means of a power lift device is driven by the power take-off shaft (PTO), the engine speed has to be adjusted such that the required power is available at the take-off-shaft and that the take-off shaft rotates with the appropriate rotational speed (xe2x80x9cstandard rotational speedxe2x80x9d) or a rotational speed as close as possible thereto. Conventionally, the engine speed, and thereby also the rotational speed of the take-off shaft, taking into account the gear used in the PTO gear box, is adjusted by means of a hand throttle lever.
In operation, the rotational speed of the power take-off shaft shall not vary to a larger extent since for instance with implements for applying seed or fertilizer, the application density has to be kept constant. On disengaging the power take-off shaft clutch, the rotational speed of the engine stays increased or increases, respectively, unless there is no counter action by the operator, for instance by moving back of the manual throttle lever. This is true for vehicles both with discontinuously or continuously variable transmissions.
A driving mechanism as set out above is known from German Patent Document DE 4.001.398. With this drive mechanism, there is a controlling connection between the engine and the power take-off shaft clutch in that the clutch is disengaged if the rotational speed of the engine decreases too far or if the associated hydraulic power lift device reaches a certain height. When the end of a furrow is reached during field work and the power take-off shaft clutch is disengaged, the manual throttle lever has to be moved back to avoid annoying noises and high fuel consumption; with vehicles having a discontinuously variable transmission, this is additionally required to reduce the traveling speed for a turning maneuver. The automatic disengagement of the power take-off shaft clutch on lifting the power lift device is known and possibly critical with respect to operational safety. Even this cannot prevent that the rotational speed of the engine is reduced or is reduced too late. This results in the fact that the universally jointed shaft connected to the power take-off shaft rotates with high speed in the lifted position with grossly angle universal joints. This increases the wear thereof and can result in the destruction thereof on fast lift-up, especially in view of the fact that with a constant pressure pump and high rotational speed of the engine the lift speed may be quite high. SUMMARY OF THE INVENTION
It is an object of the invention to avoid this disadvantages of the prior art by providing a drive controller that effects a careful and economical operation of a vehicle.
It is a feature of this invention that the drive controller issues an instruction for engaging the power take-off shaft clutch at a low rotational speed of the engine, the power take-off shaft clutch is engaged in a controlled manner, or the rotational speed of the engine is automatically reduced before engaging the power take-off shaft clutch, respectively.
It is another feature of this invention that with the full engagement of the power take-off shaft clutch, the rotational speed of the engine is automatically increased by the controller up to the rotational speed of the engine required for the nominal speed of the power take-off shaft.
It is still another feature of this invention that on disengaging the power take-off shaft clutch again, the controller automatically reduces the rotational speed of the engine.
It is an advantage of this invention that the power take-off shaft clutch may be engaged with very little wear and without much load for the driven implement (xe2x80x9csoft start upxe2x80x9d). The reduced speed of rotation of the engine is just high enough to avoid stalling of the engine on starting up the implement with a corresponding temporally controlled engagement of the power take-off shaft clutch. If the rotational speed of the engine is high at the time of issuing the command, it is reduced beforehand.
It is another advantage of this invention that the rotational speed of the engine and thereby the speed of the power take-off shaft is automatically increased to the correct value which per se results in facilitating the operation. This will take place without any frictional losses within the power take-off shaft clutch. The increase of the rotational speed of the engine further may be optimized by predetermining a temporal function (claim 9). With a discontinuously variable transmission, in this manner further the correct travelling speed is adjusted; with a continuously variable transmission, the operator may direct his full attention to the adjustment of the correct travelling speed.
It is still another advantage of this invention that the rotational speed of the engine is automatically reduced on disengaging the power take-off shaft clutch. In this manner, it is ensured that this reduction occurs, and that it occurs in due time and in the required amount. On the other hand, the slowing-down time of the take-off shaft is shortened and the risk of damages is reduced. The automatic reduction of the engine speed results in a reduction of noise emission and fuel consumption.
With a preferred embodiment, on issuing the instruction to disengage the power take-off shaft clutch, first the rotational speed of the engine is automatically reduced, and only then the power take-off shaft clutch is disengaged. The slowing-down time of the power take-off shaft is even shorter, thereby increasing the longevity and reliability. With a vehicle having a discontinuously variable transmission in the travelling drive transmission, the desired speed reduction also is obtained in due time before turning at the headlands.
If the utility vehicle has a power lift device for an implement driven by the power take-off shaft, an advantageous embodiment of the invention consists in the fact that in an automatic mode of the control, on issuing the instruction for lifting the power lift device, the power take-off shaft clutch is disengaged and the rotational speed of the engine is reduced, and on lowering again of the lift device. In this matter, firstly the convenience of the operation is increased since with only one instruction a plurality of control actions is initiated. In view of the lower rotational speed of the engine and therefore of the oil pump feeding the power lift device, the lift-up of the power lift device is performed in a slower manner. Since the lift-up speed is not controllable with conventional power lift device controllers, this is an twofold advantage.
An even more advantageous embodiment is constituted by the fact, that in an automatic mode of control, on issuing of the instruction to lift up the power lift device, as a first step the rotational speed of the engine is automatically reduced, whereupon the power take-off shaft clutch is disengaged, and only then the power lift device is lifted up, and that on lowering again of the power lift device. In addition to the advantages of the preceding paragraph, this results in the fact that on lifting the power lift device, the rotational speed of the power take-off shaft already shall have been reduced so far that there is no risk of damaging the universally jointed shaft on lifting up. The slowing-down time is even shorter in view of the preceding reduction of the rotational speed.
If the transmission is a transmission having a continuously variable transmission ratio, an additional advantage is obtained by the fact that on operation with engaged power take-off shaft clutch, the rotational speed of the engine is kept constant and the travelling speed is only controlled by the transmission ratio of the transmission. In this manner, with a constant rotational speed of the power take-off shaft, the travelling speed may be adapted to the requirements.
It is further within the scope of the invention to automatically increase the rotational speed of the engine on putting into operation of a further hydraulic load and to decrease this speed on putting out of operation of this load. By this means, the idle speed may be lowered and/or if the further load shall be operational in idle condition, the oil pump driven by the engine may have smaller dimensions. This results from the fact that on increasing the load, the rotational speed of the engine is increased.
In an advantageous embodiment wherein the hydraulic load is fed by a constant pump driven by the engine, a pressure sensor provided at the pump will issue the signal for increasing the rotational speed of the engine. In this manner, short and simple instruction paths will be obtained since the pump is mounted to the engine.
In an embodiment of the invention for a utility vehicle wherein the hydraulic load is connected to a bus system of the vehicle and is fed by a constant pump driven by the engine, said load reports its requirements via the bus system and initiates the increase of the rotational speed of the engine in the required amount, and it further reports faults and effects in this manner a reduction of the engine speed. In this manner, the rotational speed is not simply increased to a predetermined value but adapted to the type and the operational condition of the additional load. In this manner, the possibilities of a modern agricultural bus system (landwirtschaftliches Bus-System-LBS) are used to full extent.
These and other objects, features and advantages are accomplished according to the instant invention by providing a method for controlling the drive mechanism of a utility vehicle having a power take-off shaft, where the drive mechanism including an engine, a transmission, a power take-off shaft clutch and a controller, to operate the drive mechanism in a careful and economical manner. The method of controlling the engine includes the step of issuing an instruction for engaging the power take-off shaft clutch at a low rotational speed of the engine so that the power take-off shaft clutch is engaged in a controlled manner. If the rotational speed of the engine is above a threshold, the rotational speed is automatically reduced before the engaging the power take-off shaft clutch. After fully engaging the power take-off shaft clutch, the rotational speed of the engine is automatically increased until reaching of the rotational speed of the engine required for the nominal rotational speed of the power take-off shaft. When disengaging the power take-off shaft clutch, the controller automatically reduces the rotational speed of the engine.